1. Field of the Invention
This invention relates to spatial light modulation, and more particularly to systems and methods which are capable of transforming a noncoherent light beam with a given spatial intensity pattern to a coherent beam which retains the spatial intensity information.
2. Description of the Related Art
It is desirable to be able to perform optical data processing based upon a noncoherent light image. For example, the light pattern appearing on the screen of a cathode ray tube (CRT) may be manipulated, enhanced, intensified or otherwise processed by breaking down the image into a matrix of pixels, and operating upon each of the pixels individually depending upon its intensity. Other sources of noncoherent light that may be subjected to optical data processing techniques include light emitting diode and laser diode arrays, and in general any high-speed scan system, such as an accousto-optic scanner.
Optical data processing Fourier transformations and the like can be performed more readily with coherent than noncoherent beams. Accordingly, devices have been developed for transforming a spatial intensity modulation pattern on a noncoherent beam into a corresponding spatial pattern on a coherent wavefront. Such devices typically transform the spatial intensity pattern on the noncoherent beam to a spatial phase pattern on the coherent beam, such that the phase of each pixel in the coherent beam varies with the light intensity in a corresponding pixel of the noncoherent beam. An example of a device that transforms spatial noncoherent intensity modulations to coherent phase modulations is provided in the article by D. Psaltis et al., "Photorefractive Incoherent-to-Coherent Optical Conversion", Proceedings of the SPIE, Volume 465 Spatial Light Modulators and Applications, Jan. 26-27, 1984, pp. 2-8. A variety of spatial light modulators that are used to modulate a coherent beam of light from a number of different inputs are summarized in D. Casasent, "Spatial Light Modulators", Proceedings of the SPIE, Volume 465, Spatial Light Modulators and Applications, Jan. 26-27, 1984, pp. 143-157.
Current devices that perform a transformation from noncoherent intensity modulation to coherent phase modulation generally suffer from a relatively slow response time, and in addition do not exhibit optimum linearity. That is, their transfer characteristics do not produce variations in the coherent output beam that are directly proportional to variations in the noncoherent beam throughout the operating range. Furthermore, it would often be desirable to accomplish the noncoherent-to-coherent transformation by modulating the spatial intensity of the output coherent beam, rather than its spatial phase.